JP5223638B2 - Control method of optical receiver module - Google Patents

Description

  The present invention relates to a method for controlling an optical receiver module that receives an optical signal.

  In order to solve the bottleneck of the transmission capacity of server-to-server communication, the optical communication module has recently been required to expand the transmission capacity up to 100 Gbps. Up to now, for example, four transmission waves from a transmitter including an EML (Electro-absorption Modulated Laser) / DML (Direct Modulated Laser) modulated with a transmission capacity of about 26 Gbps are combined as an optical signal, and 10 km / A method of demultiplexing after transmission through a 40 km SMF (Single Mode Fiber) and receiving with four receivers on the receiving side has been studied.

  In the optical communication module as described above, since the signal loss in the SMF at the time of 40 km transmission is large, a semiconductor optical amplifier (SOA: SOA) is provided on the SMF side of the receiving side demultiplexer (ODMAX: Optical De-Multiplexer). Semiconductor Optical Amplifiers) are arranged to compensate for loss in the fiber. As a compensation method, there has been reported the possibility of realizing a wide dynamic range of optical input by controlling the SOA bias current in accordance with the optical input level to the SOA and changing the gain of the SOA. That is, when the optical input level is low, the bias current is increased to increase the gain by increasing the gain, and when the optical input level is high, the bias current is decreased (or the bias current is drawn to use the SOA as an absorption element). Therefore, it has been studied to reduce the gain of the SOA within a range that does not affect the receiving circuit provided on the output side of the duplexer.

Alternatively, as another compensation method in the optical receiver, there is disclosed a method in which a variable optical attenuator is provided in front of the SOA and the output level of the SOA is adjusted by the attenuation of the attenuator (see Patent Document 1 below), An optical communication module capable of adjusting the gain of the SOA is also disclosed (see Patent Document 2 below).
JP 2004-120669 A Japanese Patent Laid-Open No. 2005-064051

  However, in the above-described gain control method of the optical communication module, it is necessary to monitor the light intensity input to the SOA and control the SOA bias current according to the monitoring result. As a result, in order to reliably monitor the attenuated optical input signal, a circuit for branching and monitoring the optical signal tends to become large.

  Therefore, the present invention has been made in view of such problems, and an object of the present invention is to provide a method for controlling an optical receiver module capable of compensating for signal loss in a transmission path with a simple configuration.

In order to solve the above problems, a method for controlling an optical receiver module of the present invention includes a semiconductor optical amplifier that amplifies an optical signal including signals of a plurality of channels, and an optical signal amplified by the semiconductor optical amplifier for each of a plurality of channels. An optical receiving module control method comprising: an optical demultiplexing unit for branching into an optical signal; and a plurality of optical receiving units for converting an optical signal for each of a plurality of channels into an electrical signal, and monitoring an output of each of the plurality of optical receiving units Then, the gain of the semiconductor optical amplifier is controlled by adjusting the bias current supplied to the semiconductor optical amplifier based on the output, and all the outputs of the plurality of optical receiving units are within a predetermined upper limit value and lower limit value range. If a bias current is supplied so as not to change the gain of the semiconductor amplifier, and any of the outputs of the plurality of optical receivers exceeds a predetermined upper limit value, a half current is supplied. The bias current is decreased by a predetermined value so as to decrease the gain of the body amplifier, and when any of the outputs of the plurality of optical receivers falls below a predetermined lower limit value, the bias current is increased so as to increase the gain of the semiconductor amplifier. Is increased by a predetermined value .

  According to such a control method of the optical receiver module, the optical signal amplified by the semiconductor optical amplifier is branched into optical signals for a plurality of channels, and the branched optical signals are converted into electrical signals by the plurality of optical receivers. The gain of the semiconductor optical amplifier is controlled by adjusting the bias current that is converted and supplied to the semiconductor optical amplifier based on the monitoring results of the outputs of the plurality of optical receivers. By monitoring the electrical signal at the subsequent stage of the optical receiver in this way, it becomes easy to reduce the size of the monitoring circuit while realizing stable gain control, and the signal loss in the transmission line can be reduced with a simple apparatus configuration as a whole. Can be compensated.

  In this case, when used in a communication system in which a plurality of optical signals such as a WDM (Wavelength Division Multiplexing) system are combined and transmitted, even if the attenuation characteristic of any of the optical signals fluctuates, Signal loss can be compensated.

  Also, when any of the outputs of each of the plurality of optical receivers further exceeds a predetermined maximum upper limit value, or when any of the outputs of each of the plurality of optical receiver units further falls below a predetermined minimum lower limit value It is also preferable to maintain the bias current at a predetermined minimum value.

  In this way, it is possible to prevent a situation in which the optical input intensity becomes large and cause the subsequent optical receiving unit to break down, and an excessive optical signal can be recovered at the time of recovery after the optical input intensity has once decreased. Can be prevented from being input.

  Further, if any one of the outputs of each of the plurality of optical receivers exceeds a predetermined upper limit value and any of the other outputs of each of the plurality of optical receiver units falls below a predetermined lower limit value, the bias current is predetermined. It is also preferable to maintain the minimum value of.

  In this manner, by stopping the control of the gain of the optical signal when the direction of intensity variation for each of the plurality of optical signals is different, it is possible to avoid a situation in which the subsequent optical receiving unit is damaged.

  According to the control method of the optical receiver module of the present invention, it is possible to compensate for the signal loss in the transmission path with a simple configuration.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a method for controlling an optical receiver module according to the invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram showing a configuration of an optical communication system including a 4-wave WDM optical receiver module according to a preferred embodiment of the present invention. The optical communication system 1 shown in FIG. 1 is configured by connecting an optical transmission line 4 made of SMF between a 4-wave WDM optical transmission module 2 and a 4-wave WDM optical reception module 3.

  In this optical transmission module 2, four-wave optical signals modulated by four transmitters 5 a, 5 b, 5 c and 5 d with a transmission capacity of about 26 Gbps are converted into about 100 Gbps by a multiplexer (OMUX: Optical Multiplexer) 6. The optical signal is multiplexed and output toward the optical transmission line 4. The average wavelengths of the optical signals generated by the transmitters 5a, 5b, 5c, and 5d are set to, for example, 1295 nm, 1300 nm, 1304 nm, and 1309 nm.

  On the other hand, the optical receiving module 3 receives an optical signal obtained by combining optical signals for four channels from the optical transmission path 4. The optical receiver module 3 includes a semiconductor optical amplifier (hereinafter referred to as “SOA”) 7, a demultiplexer (ODMUX) 8 as an optical separator, four receivers 9 a, 9 b, 9 c, 9 d, a monitor circuit 10, and The control circuit 11 is configured.

  The SOA 7 amplifies the optical signal received from the optical transmission line 4 as it is, and sends it to the ODMUX 8 at the subsequent stage. The SOA 7 can increase or decrease the amplification factor (gain) of the optical signal in accordance with the value of the bias current supplied from the control circuit 11.

  The ODMUX 8 demultiplexes the optical signals for four channels amplified by the SOA 7 into optical signals for the respective channels. Each of these optical signals is modulated by the optical transmission module 2 with a transmission capacity of about 26 Gbps. Then, the ODMUX 8 branches and outputs the demultiplexed optical signals to the receivers 9a, 9b, 9c, and 9d.

  Each of the receivers 9a, 9b, 9c, and 9d converts the optical signal output from the ODMUX 8 into an electrical signal and outputs the electrical signal. A receiver circuit (not shown) is further connected to the subsequent stage of these receivers 9a, 9b, 9c, 9d, and the receiver circuit performs predetermined processing on the electrical signals output from the receivers 9a, 9b, 9c, 9d. Is done. Each of the receivers 9a, 9b, 9c, and 9d outputs the converted electric signal to the monitor circuit 10 that is a circuit for monitoring the electric signal.

  The monitor circuit 10 monitors the output of electrical signals from the receivers 9a, 9b, 9c, 9d, and outputs signals indicating the respective output intensity monitor values to the control circuit 11. In response to this output, the control circuit 11 controls the bias current supplied to the SOA 7.

  Specifically, the control circuit 11 includes a bias control unit 11a, a data storage unit 11b, and an external interface unit 11c. The data storage unit 11b stores parameters and control programs necessary for controlling the bias current, and the bias control unit 11a reads these parameters and programs to execute control processing. FIG. 2 is a circuit diagram showing a detailed configuration of the bias control unit 11a. The bias control unit 11a includes a calculation unit 12 and two transistors 13a and 13b as current sources switched by the calculation unit 12. One end of the SOA 7 is connected between the two transistors 13a and 13b connected in series, and a predetermined voltage Vm is applied to the other end of the SOA 7. The bias current supplied to the SOA 7 is increased / decreased by controlling the amount of current of the transistors 13a and 13b by the applied voltage from the arithmetic unit 12.

  Returning to FIG. 1, the external interface unit 11 c outputs an alarm to the outside under the control of the bias control unit 11 a when an abnormality is detected in the monitoring results of the electrical signals of the receivers 9 a, 9 b, 9 c, 9 d. .

In the data storage unit 11b, a control upper limit value V _cmax , a control lower limit value V _cmin , an absolute maximum value V _max , and an absolute minimum value V _min are stored in advance. Then, the bias control unit 11a supplies the SOA 7 with the output intensity monitor values of the receivers 9a, 9b, 9c, and 9d so as to be within the range between the control upper limit value V _cmax and the control lower limit value V _cmin. Adjust the bias current. The bias control unit 11a, the receiver 9a, 9b, 9c, either the output intensity monitor value 9d is greater than or absolute maximum value _{V max,} the, or outside in the case of less than the absolute minimum value _{V min} Outputs alarm and stops bias current control.

In addition, the data storage unit 11b also includes a minimum current value Ib _min , a minimum bias current value Ib _min0 , a maximum bias current value Ib _max0 , and a bias current control width ΔIb as parameters relating to the magnitude of the bias current set in the SOA 7. It is remembered. The bias controller 11a repeats the control to increase or decrease the value of the bias current for each amount determined by the bias current control width ΔIb in the range between the minimum bias current value Ib _min0 and the maximum bias current value Ib _max0 . Further, the bias control unit 11a has a minimum current value Ib _min as a bias current value for forcibly fixing the bias current when the module is started or when the output intensity monitor values of the receivers 9a, 9b, 9c, and 9d are abnormal. Refer to

FIG. 3 is a diagram illustrating a relationship between the output intensity monitor value and the bias current control value in the bias current control process by the bias control unit 11a. Thus, when the output intensity monitor values of the receivers 9a, 9b, 9c, and 9d are in a range between the control upper limit value V _cmax and the control lower limit value V _cmin (for example, a range of about 10 dB), The current bias current Ib is maintained. On the other hand, when any of the output intensity monitor values of the receivers 9a, 9b, 9c, and 9d exceeds the control upper limit value V _cmax , the bias current control width ΔIb is subtracted from the current bias current Ib to obtain the bias current. Ib is adjusted. When any of the output intensity monitor values of the receivers 9a, 9b, 9c, and 9d is less than the control lower limit value V _cmin , the bias current control width ΔIb is added from the current bias current Ib to obtain the bias current. Ib is adjusted. The receiver 9a, 9b, 9c, either the output intensity monitor value 9d is, if it exceeds the absolute maximum value _{V max,} or if it falls below the absolute minimum value _{V min,} the current of the bias current Ib It is forcibly fixed to the minimum current value Ib _min .

  Here, the bias current control parameters are set in advance in consideration of the allowable optical input ranges of the receivers 9a, 9b, 9c, and 9d. That is, the optical input range (dynamic) that can receive a high-speed signal without error due to the characteristics of the minimum input level (for example, -12 dBm) and the maximum input level (for example, +2 dBm) of the receivers 9a, 9b, 9c, 9d that do not use the SOA Range) is determined (bare characteristics of the receiver). Therefore, by using the SOA 7 in front of the receivers 9a, 9b, 9c, and 9d and amplifying the input light intensity and controlling the gain, a high-speed signal can be received without error in a wider optical input range (dynamic range). Thus, the parameters for controlling the bias current are selected.

  Further, when the SOA 7 is used, since the SOA 7 generates a kind of white noise called ASE (Amplified Spontaneous Emission) noise when amplifying the light, the influence of this noise (the intensity ratio between the noise and the signal light is expressed as OSNR (Optical Signal to (Noise Ratio)) must be designed. Specifically, an SOA having a small noise figure NF (Noise Figure), that is, an SOA generated by the SOA itself (including but not limited to the above ASE) is used, and the optical input level to the SOA is as high as possible. This is to design an optical system (transmission system) that is intended to have a high OSNR and receive a high-speed signal without error. On the other hand, if the output of the SOA 7 and the inputs of the receivers 9a, 9b, 9c, 9d are too large, if the SOA 7 outputs a light output intensity higher than a certain level, FWM (Four Wave Mixing: 4 waves) which is a kind of nonlinear effect Therefore, the output intensity of the SOA 7 needs to be optimally designed. Therefore, the bias current control parameter is selected in consideration of this.

  Next, the operation of the optical receiver module 3 will be described with reference to FIGS. 4 and 5 and a method for controlling the gain of the optical signal by the optical receiver module 3 will be described in detail. FIG. 4 is a flowchart showing an operation at the time of starting the optical receiving module 3, and FIG. 5 is a flowchart showing an operation at the time of gain control of the optical signal by the optical receiving module 3.

First, referring to FIG. 4, it is assumed that the optical receiving module 3 is started in a state where an optical signal is input to the SOA 7 from the optical transmission line 4 (step S101). Then, in order to prevent sudden input to the receivers 9a, 9b, 9c, 9d, the control circuit 11 sets the bias current Ib supplied to the SOA 7 to the minimum current value Ib _min (step S102). Thereafter, the monitor circuit 10 monitors the output of the electrical signals of the receivers 9a, 9b, 9c, 9d, and outputs a signal indicating the output intensity monitor value to the control circuit 11 (step S103). Then, the bias control unit 11a of the control circuit 11 determines one of the output intensity monitoring value whether exceeds the absolute maximum value _{V max} (step S104). As a result, if any of the output intensity monitoring value is determined to exceed the absolute maximum value V _max; (step S104 YES), the bias control unit 11a, the light to the outside via the external interface unit 11c An alarm relating to input is sent, and the bias current Ib is set to the minimum current value Ib _min (step S105).

In this case, the reason why the bias current Ib is set to the minimum current value Ib _min at the start-up is to prevent failure of the receivers 9a, 9b, 9c, 9d and induction of FWM. When the SOA 7 is activated with a high gain, excessive light may be input to each of the receivers 9a, 9b, 9c, and 9d depending on the light input intensity to the light receiving module 3. For this reason, the control circuit 11 controls the bias current Ib so that the gain of the SOA 7 becomes 1 or less after the activation of the module. The absolute maximum value _{V max,} the receiver 9a, 9b, 9c, 9d are set as a threshold to issue an alarm at a light intensity enough not destroyed. Specifically, the relationship with the error rate determined by the OSNR described above varies depending on the application example. However, the error rate is higher than 10 ^{−5 at} the receiver output when the minimum current value Ib _min is supplied to the SOA 7. In many cases, the absolute maximum value V _max is determined in the output range when the value is large.

On the other hand, when it is determined that all of the output intensity monitor values are equal to or less than the absolute maximum value V _max (step S104; NO), the process proceeds to FIG. 5 and shifts to a control sequence during normal operation. Here, although the gain of the SOA 7 can be controlled according to the bias current Ib, this gain has wavelength dependency. That is, as shown in FIG. 6, the relationship between the SOA bias current and the gain has a wavelength dependency, and the wavelengths of the four waves input to the receivers 9a, 9b, 9c, and 9d are 1290 to 1320 nm, respectively. In this case, when the bias current is controlled at 20 to 120 mA, the wavelength dependency of the gain changes according to the bias current. The SOA gain also depends on the polarization direction of incident light, but this value is generally smaller than the bias current dependency. In particular, in the region where the bias current is small, the polarization dependence of the SOA gain can be ignored. For example, when the bias current is 20 mA, the gain of 1320 nm is about 7 dB higher than the gain of light with a wavelength of 1290 nm, but when the bias current is 120 mA, the gain of light with a wavelength of 1290 nm is about 9 dB higher. .

In accordance with such characteristics, in the control sequence during normal operation, the control upper limit value V _cmax having a width corresponding to the wavelength dependency of SOA bias current and gain (and polarization dependency of SOA) A control lower limit value V _cmin is set in advance. The difference (width) between the control upper limit value V _cmax and the control lower limit value V _cmin is determined from the wavelength dependence of the SOA bias current and gain. In the case of the characteristics shown in FIG. 6, a difference of about 10 dB is set. Is done. The central value of the control upper limit value V _cmax and the control lower limit value V _cmin at this time is based on the error rate (for example, 10 ⁻¹² or less) required for the output of each receiver 9a, 9b, 9c, 9d from the transmission system. Is set to the optical input intensity when the error rate characteristic is sufficiently small.

In the control sequence during normal operation, first, the output of each receiver 9a, 9b, 9c, 9d is monitored again (step S201). Next, the bias control unit 11a of the control circuit 11 determines whether any output intensity monitor value exceeds the control upper limit value V _cmax (step S202).

As a result of the above determination, when it is determined that the output intensity monitor value exceeds the control upper limit value V _cmax (step S202; YES), the bias control unit 11a uses the current bias current Ib supplied to the SOA 7 as the bias current. Control is performed to decrease the control width ΔIb (step S204). Next, the bias controller 11a determines whether or not the bias current Ib is less than the minimum bias current value Ib _min0 (step S205). If the bias current Ib is _{equal to} or greater than the minimum bias current value Ib _min0 (step S205; NO) The process returns to step S201, and the output intensity is monitored again. In contrast, if the bias current Ib falls below the minimum bias current value _{Ib min0} (step S205; YES), further, whether the output intensity monitoring value of either the bias control unit 11a is greater than the absolute maximum value _{V max} It is determined whether or not (step S206). As a result, if any of the output intensity monitor values is equal to or less than the absolute maximum value V _max (step S206; NO), the bias current value Ib is set to the minimum bias current value Ib _min0 (step S208), and the process is performed in step S201. Return to. Minimum; (YES step S206), the bias control unit 11a sends out an alarm to an optical input to the external, the bias current Ib on the other hand, if any of the output intensity monitoring value exceeds the absolute maximum value V _max After setting to the current value Ib _min (step S207), the process proceeds to step S201.

In this way, when the optical input intensity value to the SOA 7 increases, the bias control unit 11a controls the bias current so that all output intensity monitor values are equal to or less than the control upper limit value V _cmax . Here, the reason why the bias current value Ib is not _lower than the minimum bias current value Ib _min0 is to prevent the deterioration of the NF of the SOA 7. Specifically, as shown in FIG. 7, the NF of the SOA 7 is deteriorated when the bias current Ib is reduced, and the purpose is to prevent it in advance. In this case, the input light level each receiver 9a, 9b, 9c, is input to 9d continues to rise following the optical input level to the SOA 7, one of the receiver exceeds the absolute maximum value V _max It can be assumed that this will happen. At that time, an optical input alarm is issued outside the optical receiving module 3.

On the other hand, if it is determined that any output intensity monitor value is equal to or less than the control upper limit value V _cmax (step S202; NO), the bias control unit 11a then determines that any output intensity monitor value is the control lower limit value V. It is determined whether it is below _cmin (step S203). As a result of the determination, if any of the output intensity monitor values is equal to or greater than the control lower limit value V _cmin (step S203; NO), the bias controller 11a maintains the current bias current Ib and returns the process to step S201. Repeat the output intensity monitor.

On the other hand, if any output intensity monitor value is below the control lower limit value V _cmin (step S203; YES), the current bias current Ib supplied to the SOA 7 is increased by the bias current control width ΔIb. Control is performed (step S209). Thereafter, the bias control unit 11a is a bias current Ib is determined whether exceeds the maximum bias current value _{Ib max0} (step S210), when the bias current Ib is equal to or less than the maximum bias current value _{Ib max0} (step S210; NO), The process returns to step S201, and the output intensity is monitored again. On the other hand, when the bias current Ib exceeds the maximum bias current value Ib _max0 (step S210; YES), the bias controller 11a further determines whether any output intensity monitor value is below the absolute minimum value _Vmin. Determination is made (step S211). As a result, if any of the output intensity monitor values is equal to or greater than the absolute minimum value V _min (step S211; NO), the bias current value Ib is set to the minimum bias current value Ib _min0 , and the process returns to step S201. On the other hand, if any one of the output intensity monitor values is below the absolute minimum value V _min (step S211; YES), the bias control unit 11a sends an alarm regarding optical input to the outside and minimizes the bias current Ib. After setting to the current value Ib _min (step S212), the process proceeds to step S201 and the monitoring of the receiver output intensity is repeated.

Thus, when the optical input intensity value to the SOA 7 decreases, the bias control unit 11a controls the bias current so that all output intensity monitor values are equal to or greater than the control lower limit value V _cmin . Here, as shown in FIG. 6, the SOA gain tends to saturate at a certain bias current or higher, and even when a bias current higher than that is applied, the power consumption only increases and the gain does not increase. Therefore, the bias current Ib is controlled so as not to exceed the maximum bias current value Ib _max0 . The bias controller 11a sets the bias current Ib to the minimum current value Ib _min when the output of any of the receivers 9a, 9b, 9c, 9d is below the absolute minimum value V _min. The minimum value V _min varies depending on the application example in relation to the error rate determined by OSNR. Normally, the absolute minimum value V _min is often set in the output range when the error rate is larger than 10 ⁻⁵ in the receiver output in a state where the minimum current value Ib _min is supplied to the SOA 7. At this time, by setting the bias current Ib to the minimum current value Ib _min, when the optical input to the SOA 7 suddenly increases due to insertion / removal of the optical fiber connector in the optical reception module 3, the receivers 9a, 9b , 9c, 9d can avoid the possibility that excessive light is input to destroy the receivers 9a, 9b, 9c, 9d.

In the control sequence during normal operation, depending on the operation mode or the state of the transmission system, it is assumed that some receivers fall below the control lower limit value V _cmin and other receivers _enter a mode exceeding the control upper limit value V _cmax. Yes. Also in this case, the bias controller 11a sets the bias current Ib to the minimum current value Ib _min and issues an alarm to the outside. Thus, by stopping the control of the gain of the optical signal when the direction of intensity fluctuation for each optical signal input to the receiver is different, it is possible to avoid a situation that causes the receiver to malfunction. .

  According to the gain control method by the optical receiver module 3 described above, the optical signal amplified by the SOA 7 is branched into optical signals for each of four channels, and the branched optical signals are divided into four receivers 9a, 9b, 9c. , 9d are converted into electric signals, and the bias current Ib supplied to the SOA 7 is adjusted based on the monitoring results of the outputs of the receivers 9a, 9b, 9c, 9d, thereby controlling the gain of the SOA 7. In this way, by monitoring the electrical signal at the subsequent stage of the receivers 9a, 9b, 9c, 9d, it becomes easy to reduce the size of the monitor circuit while realizing stable gain control, and transmission is performed with a simple apparatus configuration as a whole. Signal loss on the road can be compensated.

When all the outputs of the four receivers 9a, 9b, 9c, and 9d are within the control lower limit value V _cmin and the control upper limit value V _cmax , the bias current Ib is supplied so as not to change the gain of the SOA 7. Since the SOA gain is controlled to be adjusted when the four receivers 9a, 9b, 9c, and 9d are out of the above ranges, a plurality of optical signals such as a WDM (Wavelength Division Multiplexing) method are combined. Thus, when used in a transmitted communication method, even when the attenuation characteristic of any optical signal varies, the loss of the optical signal can be compensated stably.

Further, the bias current Ib is maintained at the minimum current value Ib _min when any of the outputs of the four receivers 9a, 9b, 9c, and 9d deviates from the absolute minimum value V _min or the absolute maximum value V _max. As a result, it is possible to prevent a situation in which the optical input intensity increases and damages the subsequent optical receiver, and an excessive optical signal is input during recovery after the optical input intensity has decreased. Can be prevented.

  Here, the effect of this embodiment will be described in comparison with a comparative example. As a comparative example for the optical communication system 1 of the present embodiment, an optical communication system 901 as shown in FIG. 9 is assumed. In the optical communication system 901 shown in the figure, an optical signal input from the optical transmission line 4 to the SOA 7 is directly monitored by the control circuit 910 in the optical receiving module 903, and the bias current of the SOA 7 is controlled according to the monitoring result. Is different from the optical communication system 1.

  As described above, the technique of directly monitoring the SOA input requires an optical branching unit and a monitor circuit for branching an optical signal to be input and inputting it to the monitor circuit, and the optical receiving module 903 tends to be large and expensive. was there. On the other hand, in the optical receiver module 3, it is easy to reduce the size of the monitor circuit, and it becomes easy to simplify the overall device configuration.

  In addition, this invention is not limited to embodiment mentioned above. For example, the bias controller 11a may employ a configuration as shown in FIG. Specifically, the bias control unit 11 a may include two pairs of transistors 13 a, 13 b, 14 a, and 14 b as current sources that are switched by the calculation unit 12, depending on the applied voltage from the calculation unit 12. The direction of the bias current supplied to the SOA 7 may be changed.

1 is a block diagram showing a configuration of an optical communication system including a four-wave WDM optical receiving module according to a preferred embodiment of the present invention. FIG. 2 is a circuit diagram illustrating a detailed configuration of a bias control unit in FIG. 1. It is a figure which shows the relationship between the output intensity monitor value and bias current control value in the bias current control process by the bias control part of FIG. 2 is a flowchart showing an operation at the time of activation of the optical receiver module of FIG. 1. 3 is a flowchart showing an operation at the time of gain control of an optical signal by the optical receiver module of FIG. 1. 2 is a graph showing the wavelength dependence of the relationship between the bias current and gain of the SOA of FIG. It is a graph which shows the wavelength dependence of the bias current of SOA of FIG. 1, and NF. FIG. 6 is a circuit diagram illustrating a modification of the bias control unit in FIG. 1. It is a block diagram which shows the structure of the optical communication system containing the 4-wave WDM optical receiving module which is a comparative example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Optical receiver module, 9a, 9b, 9c, 9d ... Receiver (optical receiver), 7 ... SOA (semiconductor optical amplifier), 8 ... ODMUX (optical separator).

Claims (3)

A semiconductor optical amplifier that amplifies an optical signal including signals of a plurality of channels; an optical separation unit that branches the optical signal amplified by the semiconductor optical amplifier into optical signals for a plurality of channels; and A method of controlling an optical receiver module comprising a plurality of optical receivers for converting an optical signal into an electrical signal,
By monitoring the output of each of the plurality of optical receivers and adjusting the bias current supplied to the semiconductor optical amplifier based on the output, the gain of the semiconductor optical amplifier is controlled ,
And supplying the bias current so as not to change the gain of the semiconductor amplifier when all the outputs of the plurality of optical receivers are within a predetermined upper limit value and lower limit value range, and the plurality of optical receiver units When any one of the outputs exceeds the predetermined upper limit, the bias current is decreased by a predetermined value so as to reduce the gain of the semiconductor amplifier, and any one of the outputs of the plurality of optical receiving units Is below the predetermined lower limit, the bias current is increased by a predetermined value so as to increase the gain of the semiconductor amplifier,
And a method of controlling the optical receiver module. When any of the outputs of each of the plurality of optical receiving units further exceeds a predetermined maximum upper limit value, or when any of the outputs of the plurality of optical receiving units further falls below a predetermined minimum lower limit value Maintains the bias current at a predetermined minimum value,
The method of controlling an optical receiver module according to claim 1 . If any one of the outputs of each of the plurality of optical receiving units exceeds the predetermined upper limit value, and any other output of each of the plurality of optical receiving units falls below the predetermined lower limit value, the bias Maintaining the current at a predetermined minimum value,
The method of controlling an optical receiver module according to claim 1 or 2 .

Images